Various machines are known in the art for removing fibers or otherwise processing papermaking stock. For example, a pulper generally includes a tub or other suitable container for holding and feeding a volume of the papermaking stock through an extraction bedplate generally located at the base or bottom of the tub. A rotor or other agitator churns or mixes the papermaking stock in the tub, causing the papermaking stock to abrasively flow over the extraction bedplate. As the papermaking stock flows over and rubs against the extraction bedplate, apertures in the extraction bedplate abrade or scrape against the papermaking stock, reducing the size of the papermaking stock and allowing the abraded stock pass through the extraction bedplate.
The size and geometry of the apertures are specifically designed to efficiently abrade and defiber the papermaking stock. For example, the size of the apertures effects the number of apertures that may be arranged on the extraction bedplate, and thus the cutting surfaces exposed to the papermaking stock. Similarly, the geometry of the apertures effects the ability of the apertures to abrade and defiber the papermaking stock without becoming obstructed. Specifically, apertures having sharp edges and/or acute angles may enhance the abrasion of the papermaking stock by forming sharp cutting surfaces. However, a trade-off exists in that sharp-edged apertures tend to dull or wear out faster, and apertures having acute corners tend to collect papermaking stock, thereby clogging or obstructing the apertures. Therefore, continued improvements in the design and orientation of the apertures in the extraction bedplate would be useful.